<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    /* 1.content 自适应高度
    2.box1 100px
    3.余下高度给box2 */
    *{
      margin: 0;
      padding: 0;
    }
    html, body{
      height: 100vh;
    }
    /* .content{
      height: 100vh;
      background-color: red;
    } */
    /* .box1{
      height: 100px;
      background-color: green;
    }
    .box2{
      /* position: absolute; /*离开文档流*/
      /*top: 100px;
      bottom: 0px; */
      /* width: 100vh; */
      /* right: 0;
      left: 0; */
      /* height: inherit;
      background-color: yellow;
    } */ 
    .content{
      display: flex;  /*方向是水平的*/
      height: 100vh;
      background-color: red;
      flex-direction: column;
    }
    .box1{
      height: 100px;
      width: 100px;
      background-color: green;
    }
    .box2{
      flex: 1;    /*主元素*/
      background-color: yellow;
    }
  </style>
</head>
<body>
  <div class="content">
    <div class="box1"></div>
    <div class="box2"></div>
  </div>
</body>
</html>